1. Field of the Invention
The present invention relates to a process for slurry-phase gasification of carbonaceous materials using ultrasonic treatment. The process of the present invention produces gaseous fuels, primarily methane and carbon dioxide, from carbonaceous materials at temperatures and pressures substantially lower than conventional thermal processes.
2. Description of the Prior Art
Theoretically, the ideal overall reaction for production of methane from carbonaceous materials proceeds as follows: EQU 2C+2H.sub.2 O CO.sub.2 +CH.sub.4.
This reaction is promoted in the desired direction at relatively low temperatures of below about 800.degree. F. In the practice of conventional thermal gasification processes, however, significant amounts of carbon monoxide and hydrogen may also be formed by means of the following simplified reaction paths: EQU C+H.sub.2 O CO+H.sub.2 EQU C+2H.sub.2 O CO.sub.2 +2H.sub.2 EQU 3C+2H.sub.2 O 2CO+CH.sub.4
Separation of the gaseous products and conversion or disposal of the undesired product gases requires extensive equipment and entails high costs, thus significantly lowering process efficiencies.
Conventional thermal processing techniques for producing gaseous products from carbonaceous materials require severe operating conditions of temperature and pressure to achieve acceptable rates of product formation. Thermal gasification techniques typically employ operating temperatures in excess of 1500.degree. F. and pressures of up to 1000 psig. Maintenance of the high temperatures and pressures required for such thermal processing techniques increases process equipment and fuel costs and reduces process efficiency. Moreover, maintenance of process operating temperatures in excess of about 800.degree. F. tends to promote secondary reactions forming undesirable product gases such as carbon monoxide and hydrogen. Even catalytic coal gasification processes which are known to the art, such as the process described in Exxon Catalytic Coal Gasification Predevelopment Program, Final Project Report, FE-2369-24, to U.S. D.O.E., Contract No. E(49-18)-2369, December, 1978, require process temperatures on the order of at least about 1200.degree. F. and elevated process pressures. Furthermore, in the practice of prior art coal gasification processes, catalyst recovery is generally very low due to reaction of the catalyst with coal ash, increasing the overall process cost.
U.S. Pat. No. 4,391,608 teaches beneficiation of ground coal in a liquid slurry subjected to ultrasonic energy at frequencies of about 20 to 40 kHz, wherein the liquid slurry preferably comprises a small amount of oil. The '608 patent teaches that maximum temperatures of less than about 170.degree. F. should be maintained during ultrasonic treatment. After beneficiation, the content. U.S. Pat. No. 4,529,506 teaches cleaning of pulverized coal in a liquid slurry containing a surfactant subjected to ultrasonic treatment.
Several U.S. Patents teach solvent extraction of carbonaceous materials utilizing ultrasonic energy. U.S. Pat. No. 3,557,337 teaches that solvent extraction of coal subjected to ultrasonic waves at frequencies of 80 kHz permits ambient temperature use of quinoline solvent. Improved solvent extraction of coal at temperatures on the order of 75.degree. to 200.degree. F. utilizing ultrasonic energy has been observed by several researchers. "Project Western Coal: Conversion of Coal into Liquids", U.S. Office of Coal Research, Res. Develop. Rep., May 18, 1970; "Means of Increasing Yield of Extracts from Mined Coal", Baranov, S.N., N.K. Neronin and G.V. Samoylenko, Physical Technical Inst., Ukrainian SSR, V.1, pgs. 24-25, Jan. 1983; "Application of Ultrasound in the Extraction of Heat-Treated Coal", Lesniak, K., KOKS, SMOLA, GAZ 25, No. 6, p. 137, June 1980. Solvent extraction of organic materials from peat using ultrasonic waves at frequencies of 22 kHz has been demonstrated to provide increased yields and reaction rates. "Investigation of the Influence of Ultrasound on the Yield, Composition, and Properties of Peat Bitumens", Novichkova, Smirnova, Gurinova, Kalinin Polytech Inst., USSR Solid Fuel Chem., 9, No. 6, p. 64, 1975. Solvent recovery of oil from tar sands using ultrasonic waves at frequencies of 20 kHz has also been investigated. "Putting Chemical Reactions on a Sound Footing", G. M. Graff, Chemical Engineering, March, 1985. U.S. Pat. No. 4,304,656 teaches extraction of shale oil from oil shale by compression and ultrasonic treatment at frequencies of 20 kHz.
U.S. Pat. No. 2,777,813 teaches production of water-gas from pulverized coal reacted in a gas stream using sonic energy at frequencies of about 2 to 7 kHz. The '813 patent teaches reduced production at increased frequencies of 20 kHz.
U.S. Pat. No. 4,108,759 teaches thermal gasification of coal with superheated steam in the presence of heat at 1800.degree. to 2000.degree. F. producing hydrogen for hydroliquefaction of pulverized coal in a slurry of an organic hydrogenating liquid, such as hydrophenanthrene, in an oxygen-free liquefier vessel maintained at 350.degree. to 750.degree. F. under pressures of 750 to 2000 psi and utilizing ultrasonic energy at a very specific frequency matching the relaxation frequency of components of the liquid product oil.